Iceland's Major Volcanic Eruption Reveals How Sulfur Particles Influence Clouds

Iceland's volcanic eruptions may be telling scientists a bit more about clouds. Researchers have found how sulfur particles from eruptions actually influence clouds.

While humans have pumped sulfur into Earth's atmosphere since the Industrial Revolution, it's been hard to measure how this affects the clouds above. Now, researchers have used a huge volcanic eruption in Iceland to measure the change.

The researchers took advantage of a unique geologic event. During six months from summer 2014 to early 2015, a crack in the Bardarbunga volcano seeped lava and sulfur gas. This was not one of Iceland's explosive eruptions, but was instead a long, slow, low-elevation seep of sulfur emissions that produced an amount of lava second only to Laki in the recent history of Iceland eruptions.

The researchers looked at data for the region recorded by NASA's MODIS instrument to measure the size of droplets in the marine cloud layer. The researchers found that while the volcano was spewing sulfur, the droplets were the smallest in the 14-year record of observations.

"You can see the effect over an entire ocean for a two-month period," said Daniel McCoy, one of the researchers, in a news release. "It was a pretty unique geophysical event within the satellite record."

The results confirm that volcanoes cool the planet not just by emitting particles high in the atmosphere, but also by releasing low-level sulfur to influence cloud formation. When the air contains aerosol particles, the same amount of water vapor condenses into many small drops, whose larger surface area reflects more sunlight.

"One of the big uncertainties regarding climate change is how much human-produced aerosols have offset the warming until now," said Dennis Hartmann, one of the researchers. "We hope the data from this eruption will improve the model simulations of cloud effects, and narrow the uncertainties in projections of the future."

The findings are published in the journal Geophysical Research Letters.

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